1. Field of the Invention
The invention relates to actuators for a charge-cycle device.
2. Discussion of Background
Electromagnetic actuators for activating charge-cycle valves usually have two switching magnets, an opening magnet and a closing magnet, between whose pole faces an armature is arranged so as to be displaceable coaxially with respect to an axis of the charge-cycle valve. The armature acts on a valve stem of the charge-cycle valve directly or via an armature bolt. In the case of actuators according to the principle of the oscillating mass, a prestressed spring mechanism, usually two prestressed compression springs, acts on the armature, specifically an upper and a lower valve spring. The upper valve spring acts in the opening direction and the lower valve spring acts in the closing direction of the charge-cycle valve. When the switching magnets are not energized, the armature is held by the valve springs in an equilibrium position which preferably corresponds to the geometric centre between the switching magnets.
When the actuator is started, the closing magnet or the opening magnet is briefly overexcited or the armature is made to oscillate by means of an oscillation-excitation routine in order to attract the armature out of the equilibrium position. In the closed position of the charge-cycle valve, the armature bears against the pole face of the energized closing magnet and is held by it. The closing magnet prestresses the valve spring acting in the opening direction. In order to open the charge-cycle valve, the closing magnet is switched off and the opening magnet is switched on. The valve spring acting in the opening direction accelerates the armature beyond the equilibrium position so that the latter is attracted by the opening magnet. The armature strikes against the pole face of the opening magnet and is held tight by it. In order to be able to close the charge-cycle valve again, the opening magnet is switched off and the closing magnet is switched on. The valve spring acting in the closing direction accelerates the armature beyond the equilibrium position to the closing magnet. The armature is attracted by the closing magnet, strikes against the pole face of the closing magnet and is held tight by it.
Variables which have not been taken into account from the start onwards or which change over time, such as for example fabrication tolerances of individual components, thermal expansion of different materials etc., may lead to a situation in which the armature no longer completely comes to bear against the pole faces of the magnets, play arises between the armature plunger and the valve stem and/or the charge-cycle valve no longer completely closes.
From application, DE 19 647 305.5, a play-compensation element is known in which an actuator is floatingly mounted in a cylinder head. The actuator opens and closes a charge-cycle valve by means of an armature and two electromagnets which are arranged on either side in the direction of movement of the armature. On the side facing away from the charge-cycle valve there is between a cover plate and the actuator a play-compensation element which compensates both positive and negative valve play.
The play-compensation element has a first hydraulic element with a play-compensation piston in a cylinder. The play-compensation piston lies between a first pressure space, which is controlled as a function of the internal combustion engine and faces away from the charge-cycle valve, and a second pressure space which faces the charge-cycle valve. In the piston there is a non-return valve which is held in the closed position by means of a retaining spring. The non-return valve opens in the direction of the second pressure space when there is excess pressure in the first pressure space. The retaining spring is configured in such a way that the non-return valve cannot open if there is no play present, and thus closes the connection between the two pressure spaces.
Between the play-compensation piston and the cylinder there is a defined amount of play as a throttle connection through which pressure medium can escape to the outside from the second pressure space. The play-compensation element is supported on the upper cover plate which is permanently connected to the cylinder head. The play-compensation element can only transmit compressive forces.
If the charge-cycle valve does not close correctly because the actuator is displaced too far in the direction of the charge-cycle valve, i.e. there is negative play, a pressure increase comes about in the second pressure space as a result of a valve spring of the charge-cycle valve which acts in the direction of the closed position. This pressure increase has the effect that the pressure medium can escape from the second pressure space via the throttle connection, specifically until the charge-cycle valve closes completely again.
If the charge-cycle valve closes correctly, but there is play between the armature plunger and the charge-cycle valve, the valve spring of the charge-cycle valve no longer acts on the second pressure space. The pressure in the second pressure space thus drops below that in the first pressure space with the result that the non-return valve opens counter to the retaining spring. Pressure medium flows from the first pressure space into the second pressure space until the play is compensated. This compensation takes place over a plurality of working cycles of the valve.
The play-compensation element is pushed into just one hole in the actuator so that both parts can be displaced with respect to one another and are therefore easy to mount. The actuator is relieved of loading by a reaction force in the direction of the charge-cycle valve during the entire time in which the closing magnet is activated in order to close the charge-cycle valve. In addition, the play-compensation element is relieved of loading as soon as the armature strikes against the pole face of the opening magnet. When the play-compensation element is relieved of loading, it expands. If the actuator of the charge-cycle valve opens, an opposed reaction force comes about and the play-compensation element is blocked with respect to the force in accordance with its function and can only slowly yield. It may happen that the play-compensation element expands more and more, and the charge-cycle valve no longer closes completely. A type of surging effect is produced. The result of this may be, for example, that the charge-cycle valve no longer closes correctly and in the process burns. Furthermore, the switching magnet may require an increased level of energy in order to attract the armature out of its off-centre position. In addition, a so-called stroke loss occurs in which the actuator is displaced counter to the movement of the charge-cycle valve during the closing procedure.
According to a further variant from the prior art, the play-compensation element is permanently connected to the actuator and can thus absorb tensile forces and compressive forces. The play-compensation element of this second variant has, in addition to the first hydraulic element, a second hydraulic element with a cylinder in which the first cylinder is guided with a ring-like expanded portion. The ring-like expanded portion serves at the same time as a separating piston between an upper and a lower pressure chamber which are connected via an annular throttle gap. For the rest, the play-compensation element is of the same design as the variant which has been described previously.
If the charge-cycle valve is closed by means of the actuator, the reaction force is transmitted to the lower pressure chamber via the first cylinder. Since the reaction force lasts only a brief time, there is no significant compensation of pressure medium between the. upper pressure chamber and the lower pressure chamber. The actuator does not move. However, positive and negative play can be compensated over a plurality of valve cycles.
For reasons of space, the charge-cycle valves are installed in a skewed arrangement in which they diverge from one another in the direction of the actuator. One cover plate with seals and screw set must be provided per charge-cycle valve and actuator.
The valve springs displace the actuator slowly upwards when the switching magnets are not energized, as a result of which the armature is displaced out of its geometric centre position between the pole. faces of the switching magnets. In the case of the play-compensation element which can be subjected to tensile and compressive loading, depending on its function the second hydraulic element can become locked back into the centre -position, against rapid compensation. The centre position is reached only after a plurality of cycles under certain circumstances. This results in turn, for example, in an increased energy requirement and the risk of not being able to hold the charge-cycle valve because it strikes against the pole face of the closing magnet with an excessively high speed, and bounces off it again or is not accelerated sufficiently closely to the opening magnet by the upper valve spring.
DE 33 11 250 A1 discloses a device for activating a charge-cycle valve with an electromagnetic actuator in which arranged between an armature and a valve stem is a play-compensation element which can transmit only compressive forces. The play-compensation element is hermetically sealed off and does not have a pressure port via which it is supplied with pressure medium.
Patent application DE 196 24 296 A1 discloses a device for activating a charge-cycle valve with an electromagnetic actuator in which a play-compensation element is arranged between an armature plunger and a valve stem. The play-compensation element is inserted into a cup plunger which is arranged between the armature plunger and the valve stem and which is itself guided in a baseplate of the actuator casing so as to be displaceable in the axial direction of the valve. An oil supply duct, which is connected to the hydraulic play-compensation element via a circumferential groove on the cup plunger and a lateral hole runs in the baseplate.
The supply of the pressure media is a problem in the known play-compensation elements. According to DE 196 24 296 A1, the media are supplied laterally through the cup plunger which has to be guided in the baseplate with seals. The structural possibilities of supplying the pressure media in such a way are limited. Furthermore, guiding the cup plunger in a sealed fashion brings about additional or increased friction in the guide faces.
The object of the present invention consists in designing a charge-cycle device with a play-compensation element in such a way that the pressure media can be supplied in a way which is improved in terms of the friction conditions or the structural possibilities.
According to the invention, a hydraulic play-compensation element is connected to a pressure port by means of a duct in the longitudinal direction in the armature plunger. The pressure medium is supplied via a suitable transfer point to the armature plunger and from there via the duct to the play-compensation element. This measure makes it possible for the location where the pressure medium is fed to be displaced between a stationary housing component and a component of the play-compensation element which moves with the charge-cycle valve, for example to any desired locations of the armature plunger.
Preferably, the play-compensation element is used without guidance. As a result, the friction influences of the guidance of the play-compensation element, for example the energy which is dissipated by the friction and/or adhesion/sliding effects between the guide and the play-compensation element, which can give rise to deviations from the desired movement of the valve, are dispensed with.
According to a further refinement of the invention, it is proposed that the play-compensation element should be connected to the pressure port only in the area just in front of the closed position and in the closed position. The length dimension which is equivalent to how far the play-compensation element must expand, in the first instance, for the charge-cycle valve to form a good seal, with its valve plate, against the valve seat ring and, in the second instance, for the armature to come to bear precisely on the pole face of the closing magnet is obtained only if the charge-cycle valve is closed, i.e. bears with its valve plate against a valve seat ring.
Further details of the invention and the resulting advantages can be found in the following description of exemplary embodiments. Numerous features are presented as described in conjunction in the description and in the claims. The person skilled in the art will expediently also consider the features individually and combine them to form further useful combinations.